Selective bed-load transport in Las Vegas Wash, a gravel-bed stream

Bed-load measurements collected at the Las Vegas Wash, a gravel-bed stream near Las Vegas, Nevada, were used to study selective transport of sand and gravel in uni-modal or weakly bi-modal river sediment. Measurements showed that size selectivity in a sediment mixture decreases as shear stress increases. Transport of variously sized sediment particles approaches equal mobility as the transported bed load is composed approximately of the same size particles as surface-bed material. Consequently, a hiding function was derived to account for the increase or reduction in reference shear stress for an individual size class in a sediment mixture as compared with that in an uniformly sized sediment. An empirical equation for determining fractional bed-load transport rate was then formulated by correlating the dimensionless, fractional bed-load transport rate with the dimensionless bed-shear stress. This equation indicated that the hiding function depends not only on the size of individual size class but also on the flow depth used to quantify the magnitude of shear stress. The present study contributes to the body of knowledge used in predicting selective transport of sediment mixtures in gravel-bed streams. (C) 2007 Elsevier B.V. All rights reserved.